A quadrupole mass spectrometer separates ions with different masses by applying a DC voltage and an rf voltage on four rods having circular or hyperbolic cross sections and an axis equidistant from each rod. Sample ions enter this cross sectional area through an aperture at the ends of the rods. The variation of the applied rf voltages on the four rods selects sample ions of a certain mass-to-charge ratio (m/e) to exit the quadrupole mass spectrometer to be detected. Sample ions with different m/e values either impact the rods and are neutralized or deflected away from the axis of the quadrupole.
A miniature quadrupole mass spectrometer array is described in U.S. Pat. No. 5,596,193, the disclosure of which is herein incorporated by reference.
FIG. 1 shows a block diagram of a typical prior art quadrupole mass spectrometer 100 constructed of 16-rod electrodes 106 in a 4.times.4 array to form nine separate quadrupole regions. Ionization of a gas sample begins in an ionizer chamber within an ionizer 102. Sample atoms or molecules are injected into this chamber where they are intercepted by electron beams and are ionized to positive ions. These are then extracted through the entrance apertures 104 of the quadrupole mass spectrometer 100 and are detected.
Electron ionizers, as used in mass spectrometers, have applications in environmental monitoring, semiconductor etching, residual gas analysis in laboratory vacuum chambers, monitoring of manufacturing plants against toxic substances, protection of buildings, harbors, embassies, airports, military sites, and power plants against terrorist attacks.